Geomagnetic pole reversal is a "regular" phenomenon on Earth. Although the interval pattern has been irregular at times (sometimes with millions of years of difference between change intervals), Earth has settled in the last 20 million years into a pattern of a pole reversal about every 200,000 - 300,000 years (source: NASA). Based on this pattern and the fact that the most recent pole-switch occurred ~780,000 years ago, the Earth is "overdue" for a pole switch.
My question: How quickly does a pole switch occur?
Is it instantaneous? Does it take years? Millennia?
Is the current movement of the pole part of a drawn-out switch, or is it just "normal" pole movement? Again, from NASA:
The magnetic north pole has been creeping northward – by more than 600 miles (1,100 km) – since the early 19th century, when explorers first located it precisely. It is moving faster now, actually, as scientists estimate the pole is migrating northward about 40 miles per year, as opposed to about 10 miles per year in the early 20th century.
From some previous research, it seems like it doesn't always make a "clean" switch either, with multiple poles appearing globally -- would this multi-pole extravaganza increase the switching time, or is it also normal?